EP2656408B1 - Actuator system, and control of an actuator - Google Patents

Description

Actuators, such as multilayer actuators, are used in various fields, such as injection systems for engines. Actuators include piezo elements that expand when a voltage is applied. For injection systems, actuators with ever faster switching times and higher strokes are desired. Both requirements are contradictory: higher strokes require longer actuators because of the maximum ductility of the ceramic in the actuators. The speed at which the actuator expands depends on the speed of sound in the actuator. Due to the limited speed of sound in the actuator and its switching times are longer with increasing length of the actuator. The strain spreads within the actuator in the form of an elastic wave. Each individual domain, ie each expanding piezoelectric element, is the source of a partial wave. These ultimately overlap to a total deformation. Due to the different maturities of the partial waves from the place of their formation to the actuator head even at ideal steep driving voltage of the actuator results in a minimum edge time of Aktordehnung, that is, the time until the actuator has expanded, which can not be exceeded for physical reasons.

Two methods of achieving higher strokes, despite the limitations mentioned above, use relatively short actuators and, as a result, have short switching times. The strokes or required travel can be achieved by mechanical translation by means of a rocker arm or by mechanical Translation can be achieved by means of a hydraulic amplifier.

The JP 223315 A shows an actuator with a segmented outer electrode, the segments are controlled separately. This control makes it possible to control the actuator between more than two expansion stages.

The JP 1093184 A shows an actuator with segmented outer electrodes, which allow a coarse and fine adjustment of the change in length of the actuator.

The JP 63120480 A shows an actuator with segmented outer electrodes. This arrangement allows to control the actuator between more than two expansion stages.

The DE 19802302 A shows an actuator with rectangular cross-section, the outer electrodes has on the four outer sides. This arrangement reduces cracking and improves heat dissipation.

It is an object to provide an improved in terms of the above aspects actuator.

The object is achieved by an actuator having the features of patent claim 1.

There is provided an actuator system with a control arrangement and an actuator, wherein the actuator is expandable in a predetermined direction.

The actuator is arranged with stacked piezo elements, first and second internal electrodes, which are alternately arranged between the piezoelectric elements, a first external electrode, which is electrically conductively connected to the first internal electrodes, and a second Outer electrode which is electrically conductively connected to the second internal electrodes, is provided. The actuator comprises a plurality of actuator sections with a first actuator section which is arranged in the predetermined direction relative to a second actuator section. The second outer electrode comprises separate electrode segments which are each electrically conductively connected to the second internal electrodes in one of the actuator sections or in a group of the actuator sections.

By means of the control arrangement, a first drive signal at the first actuator section or a first group of actuator sections and a second drive signal can be applied at a time offset to the second actuator section or a second group of actuator sections. The control arrangement is adapted to apply the first control signal to the first actuator section or the first group of actuator sections with a time delay to the second control signal at the second actuator section or the second group of actuator sections, so that the extension of the actuator in the respective Aktorabschnitten or groups of Aktorabschnitten through superimpose the control signals generated elastic partial waves.

Each actuator section is electrically connected only to a part of the second internal electrodes. The separate, non-contacting or not directly electrically conductive interconnected electrode segments allow the Aktorabschnitte offset in time, so that the stretching process is not set for all piezo elements at the same time in motion, but offset in time.

The actuator comprises a plurality of sections, each with piezo elements and internal electrodes, which are actuated with a time delay become. The control is not carried out simultaneously for all areas of the entire actuator, but takes place with a time delay for their individual sections. Advantageously, the time offset is chosen so that it corresponds exactly to the speed of sound in the actuator. This will interfere with the Extending the actuator, the elastic partial waves such that there is a much shorter edge time for the expansion of the actuator than would be the case with simultaneous control of the outer electrode. The lower limit of the edge time is no longer limited by the length of the entire actuator, but by the length of the individual areas.

Further advantageous embodiments of the invention are specified in the dependent claims.

In one embodiment, the first outer electrode also comprises separate electrode segments which are each electrically connected to only a part of the first inner electrodes, namely to the first inner electrodes in one of the actuator sections or in a group of the Aktorabschnitte. The provision of two segmented outer electrodes allows greater degrees of freedom in the design of the actuator. The division of the segments in the first and second outer electrode may coincide. Alternatively, the segmentation is asymmetric.

In one exemplary embodiment, the electrode segments are each electrically conductively connected to either the first or the second internal electrodes in adjacent actuator sections. With segmented first and segmented second outer electrodes, this enables a first electrode segment of the first outer electrode to be electrically conductively connected to the first inner electrodes in a first actuator section and a second actuator section adjacent to the first, and a second electrode segment of the second outer electrode to be connected to the second inner electrodes in FIG second actuator section and in a third, the second adjacent Aktorabschnitt is electrically connected. In other words, the first and second outer electrodes are arranged offset from one another in such a way that they electrically conductively contact both inner electrodes in the same and in different actuator sections.

In one embodiment, at least the electrode segments of the second outer electrode each comprise a terminal to which a drive signal can be applied. The time-offset control signals enable the time-offset control of the actuator sections. With segmented first outer electrode, their segments also have terminals.

An actuator system comprises an actuator and a control arrangement, by means of which a first control signal to one of the Aktorabschnitte and a second control signal is time-shifted applied to a further Aktorabschnitt.

The actuator can expand in one direction, for example due to its fixation on the actuator base. A first actuator section is arranged in this direction relative to a second actuator section, wherein the control arrangement is adapted to apply the first drive signal to the first actuator section with a time delay to the second drive signal at the second actuator section.

If only one segmented outer electrode is provided, the control arrangement applies the control signals to its electrode segments and the other outer electrode can be connected to a reference potential. In the case of two segmented outer electrodes, the control arrangement is suitable, the electrode segments connected to the first inner electrodes and the electrode segments connected to the second Internal electrodes are connected to apply voltages of different signs with respect to a reference potential. The application of different control signals on both outer electrodes allows a better, more flexible control of the actuator.

The time offset is selected as a function of the speed of sound in the actuator to compensate for runtime differences of the partial waves.

A control of an actuator with stacked arranged piezo elements, first and second internal electrodes, which are arranged alternately between the piezo elements, wherein the actuator comprises a plurality of actuator sections, is defined in claim 8. Between the first and the second internal electrodes, in a first actuator section or a first group of actuator sections, a drive voltage is applied in a time-delayed manner to a drive voltage between the first and the second internal electrodes in a second actuator section or in a second group of actuator sections such that the first drive signal is applied The first actuator section or the first group of actuator sections is delayed in time relative to the second control signal at the second actuator section or the second group of actuator sections, so that superimposed in the respective Aktorabschnitten or groups of Aktorabschnitten generated by the control signals elastic partial waves.

The actuator expands in one direction, wherein the first actuator portion is disposed in the direction relative to the second actuator portion, and wherein the first drive voltage to the second drive voltage is time-delayed. The invention will be explained below with reference to the drawings by means of exemplary embodiments.

Figur 1

ein Ausführungsbeispiel eines Aktors ohne segmentierte Außenelektroden,

Figur 2

den zeitlichen Verlauf der Ansteuerspannung für diesen,

Figur 3

ein Ausführungsbeispiel eines Aktors mit einer segmentierten Außenelektrode,

Figur 4

eine perspektivische Ansicht desselben,

Figur 5

eine schematische Schnittdarstellung desselben,

Figur 6

den zeitlichen Verlauf der Ansteuerspannungen, die an den Elektrodensegmenten anliegen,

Figur 7

ein weiteres Ausführungsbeispiel eines Aktors mit zwei segmentierten Außenelektroden,

Figur 8

den zeitlichen Verlauf der Ansteuerspannungen, die an den Elektrodensegmenten anliegen,

Show it:

FIG. 1

An embodiment of an actuator without segmented outer electrodes,

FIG. 2

the time course of the drive voltage for this,

FIG. 3

an embodiment of an actuator with a segmented outer electrode,

FIG. 4

a perspective view of the same,

FIG. 5

a schematic sectional view of the same,

FIG. 6

the time profile of the drive voltages applied to the electrode segments,

FIG. 7

Another embodiment of an actuator with two segmented outer electrodes,

FIG. 8

the time profile of the drive voltages applied to the electrode segments,

FIG. 1 shows a schematic sectional view of a conventional multilayer actuator 1 with stacked arranged piezo elements 16. First internal electrodes 5 and second internal electrodes 3 are arranged alternately between the piezo elements 16. The first internal electrodes 5 are electrically conductively connected to a first external electrode 4. The second internal electrodes 3 are electrically conductively connected to a second external electrode 2. The first and second inner electrodes 5 and 3 are each guided to an outer side of the actuator 1 and are electrically conductively connected there to the first outer electrode 4 and the second outer electrode 2, respectively. This can be done, for example, by printing a metal paste or by soldering metallic plates, which form the outer electrodes 4, 2.

The first outer electrode 4 is connected to a reference potential 7. A control arrangement 6 applies to the second outer electrode 2 a drive signal, for example a time-variable drive potential, so that a drive voltage U lies between the first and second inner electrodes, as a function of which the actuator 1 is stretched or compressed.

FIG. 2 shows by way of example the course of a drive signal, or voltage, U as a function of the time t. The rise of the signal U has a finite slope.

By applying the drive voltage U, the actuator 1 experiences a stroke. The expansion of the actuator 1 takes place in finite time. The strain propagates within the actuator 1 in the form of an elastic wave. Each individual domain, or piezoelement 16, is the source of a partial wave. These overlap, resulting in the overall deformation. Due to the different transit times of the partial waves from the place of their formation to the actuator head results in infinitely steep control time, which requires the elongation process, which can not be exceeded for physical reasons. The longer the actuator 1 and the larger the stroke, the larger this time is.

FIG. 3 shows an embodiment of a multilayer actuator 1 having a first outer electrode 4 and a segmented second outer electrode 2, which has separate electrode segments 21, 22, 23. The separate electrode segments 21, 22, 23 are spatially separated from each other. They are neither direct electrically connected with each other, they still touch each other. The first outer electrode 4 is connected to a reference potential 7. The electrode segments 21, 22, 23 each have a terminal 210, 220, 230, via which they are connected to a control arrangement 6. Control signals can be applied via the terminals 210, 220, 230.

FIG. 4 shows the actuator system with the actuator 1 and the control arrangement 6 in a three-dimensional representation.

FIG. 5 shows a schematic sectional arrangement of the actuator 1. The actuator 1 comprises first and second internal electrodes 5, 3, which are electrically conductively connected to the first external electrodes 4 and the second external electrodes 2, respectively. The actuator 1 comprises a plurality of actuator sections 81, 82, 83. Each axially extending actuator section 81, 82, 83 corresponds to the axial extent of the electrode segments 21, 22, 23. The first electrode segment 21 is electrically conductive with the second internal electrodes 3 in FIG first actuator section 81 connected. The second electrode segment 22 is electrically conductively connected to the second internal electrodes 3 in the second actuator section 82. The third electrode segment 23 is electrically conductively connected to the second internal electrodes 3 in the third actuator section 83. By contrast, the first internal electrodes 5 in the three actuator sections 81, 82, 83 are electrically conductively connected to the same first, continuous external electrode 4.

FIG. 6 schematically shows the time course of the drive signals or the voltages U1, U2, U3, which abut the electrode segments 21, 22, 23 of the actuator 1. At the terminal 210 of the first electrode segment 21 is applied to a first drive voltage U1. At terminal 220 of the second Electrode segment 22 is applied to a second drive voltage U2. At the terminal 230 of the third electrode segment 23 is applied to a third drive voltage U3. The drive voltages U1, U2, U3 are time-delayed, so that the actuator sections 81, 82, 83 are actuated later, the closer they are to the actuator head. The actuator 1 is fixed to the actuator base or third actuator section 83. In other words, one Aktorabschnitt 81, 82, 83, which is arranged in the direction of Aktordehnung relative to another, is delayed controlled: First, the third Aktorabschnitt 83, then the second Aktorabschnitt 82, then the first Aktorabschnitt 81 is driven. The time offset is chosen so that it corresponds to the speed of sound in the actuator 1. In this case, the individual partial waves of the actuator sections 81, 82, 83 are superimposed in such a way that a substantially shorter expansion time results. The lower limit is no longer limited by the actuator length, but by the length of the individual actuator sections 81, 82, 83.

FIG. 7 shows a further embodiment of an actuator 1 with a segmented first outer electrode 4 and a segmented second outer electrode 2. The first outer electrode 4 has a first, a second and a third electrode segment 41, 42, 43, in this case, different lengths. The second outer electrode 2 has a first, a second and a third electrode segment 21, 22, 23, in this case of different lengths. The actuator sections 81, 82, 83, 84, 85 extend axially between incisions between the electrode segments 21, 22, 23, 41, 42, 43. The actuator 1 is fixed to the actuator foot or fifth actuator section 85. Of the internal electrodes to which each electrode segment 21, 22, 23, 41, 42, 43 is electrically connected, two are positioned at the edge, namely the upper and lower inner electrode, which are electrically conductively connected to the electrode segment 21, 22, 23, 41, 42, 43. The Aktorabschnitte 81, 82, 83, 84, 85 extend between two adjacent edge-mounted inner electrodes, which may be electrically conductively connected to the same or with different electrode segments 21, 22, 23, 41, 42, 43. The first actuator section 81 extends axially along the first electrode segment 41 of the first outer electrode 1. The second actuator section 82 extends axially from the edge-positioned inner electrode of the second electrode segment 42 of the first outer electrode 1 to that of the first electrode segment 21 of the second outer electrode 2 the segments 41, 42, 43 of the first outer electrode are arranged so that they are offset relative to the electrode segments 21, 22, 23 of the second outer electrode 2, the electrode segments 21, 22, 42, 43 with the inner electrodes of adjacent Aktorabschnitte 81, 82nd , 83, 84, 85 electrically conductively connected. Thus, for example, the first electrode segment 21 of the second outer electrode 2 is electrically conductively connected to the second inner electrodes of the first and second Aktorabschnitts 81, 82 electrically conductive. The second electrode segment 42 of the first outer electrode 4 is electrically conductively connected to the first inner electrodes 5 in the second and third Aktorabschnitt 82, 83 electrically conductive.

FIG. 8 shows the time course of the control signals or reference potentials with respect to a reference potential, U1, U2, U3, U4, U5, U6, of the control arrangement 6 in FIG. 7 to be provided. The first drive voltage U1 is applied to the terminal 410 of the first electrode segment 41 of the first outer electrode 4. The third drive voltage U3 is on Terminal 420 of the second electrode segment 42 of the first outer electrode 4 at. The fifth drive voltage U5 is applied to the terminal 430 of the third electrode segment 43 of the first outer electrode 4. The second drive voltage U2 is applied to the terminal 210 of the first electrode segment 21 of the second outer electrode 2. The fourth drive voltage U4 is applied to the terminal 220 of the second electrode segment 22 of the second outer electrode 2. The sixth drive voltage U6 is applied to the terminal 230 of the third electrode segment 23 of the second outer electrode 2. The signs of the first, third, fifth drive voltage U1, U3, U5 are opposite to the sign of the second, fourth and sixth drive voltage U2, U4, U6.

By increasing the sixth drive voltage U6, the fifth actuator section 85 is initially driven. As the fifth drive voltage U5 rises, which is applied to the third electrode segment 43 of the first outer electrode 4, both the voltage between the first and second inner electrodes 5, 3 of the fifth actuator section 85 is increased as the potential difference increases, as well as started, the fourth actuator section 84 to drive. With increase of the fourth drive voltage U4, which is applied to the second electrode segment 22 of the second outer electrode 2, both the voltage between the first and second internal electrodes 5, 3 of the fourth actuator section 84 is increased, as the potential difference increases, as has begun, the third actuator section 83 to drive. This activation is continued successively for the other actuator sections.

The non-edge actuator sections 82, 83, 84 are due to the overlapping arrangement of the segments 21, 22, 23, 41, 42, 43 of the outer electrodes 4, 2 are each driven in two steps.

It should be noted that the timing of the voltage rises or drops at the terminals 210, 220, 230, 410, 420, 430 for strain and compression is the same, the voltage rises or drops at individual terminals 210, 220, 230, 410, 420, 430 differ in terms of their sign when stretched and compressed.

It should be noted that the features of the embodiments can be combined.

reference numeral

1

actuator

4, 2

outer electrode

5, 3

inner electrode

6

control arrangement

7

reference potential

16

piezo element

21, 21, 23, 41, 42, 43

electrode segment

81, 82, 83, 84, 85

actuator section

210, 210, 230, 410, 420, 430

terminal

Claims (10)

1. Actuator system comprising a control arrangement (6) and an actuator (1), wherein the actuator (1), which is expandable in a predefined direction, comprises

   - piezoelements (16) arranged in a stacked fashion,

   - first and second internal electrodes (5, 3) arranged alternately between the piezoelements (16),

   - a first external electrode (4), which is electrically conductively connected to the first internal electrodes (5),

   - a second external electrode (2), which is electrically conductively connected to the second internal electrodes (3),

   - a plurality of actuator sections (81, 82, 83, 84, 85) comprising a first actuator section (81, 82, 83, 84, 85), which is arranged in the predefined direction relative to a second actuator section (81, 82, 83, 84, 85), wherein the second external electrode (2) comprises separate electrode segments (21, 22, 23), which are electrically conductively connected in each case to the second internal electrodes (3) in one of the actuator sections (81, 82, 83, 84, 85) or in a group of the actuator sections (81, 82, 83, 84, 85),
   characterized in that, by means of the control arrangement (6), a first control signal (U1, U2, U3, U4, U5, U6) can be applied to the first actuator section (81, 82, 83, 84, 85) or a first group of actuator sections (81, 82, 83, 84, 85) and a second control signal (U1, U2, U3, U4, U5, U6) can be applied in a time-shifted manner to the second actuator section (81, 82, 83, 84, 85) or a second group of actuator sections (81, 82, 83, 84, 85) in such a way that the first control signal (U1, U2, U3, U4, U5, U6) is at the first actuator section or the first group of actuator sections in a time-delayed manner with respect to the second control signal (U1, U2, U3, U4, U5, U6) at the second actuator section or the second group of actuator sections, so that the elastic partial waves generated by the control signals during the expansion of the actuator in the respective actuator sections or groups of actuator sections are superimposed.
2. Actuator system according to Claim 1,
   characterized in that
   the first external electrode (4) comprises separate electrode segments (41, 42, 43) which are electrically conductively connected in each case to the first internal electrodes (5) in one of the actuator sections (81, 82, 83, 84, 85) or in a group of the actuator sections (81, 82, 83, 84, 85).
3. Actuator system according to Claim 1 or 2,
   characterized in that
   the electrode segments (21, 22, 23, 41, 42, 43) are electrically conductively connected in each case to either the first or the second internal electrodes (5, 3) in adjacent actuator sections (81, 82, 83, 84, 85).
4. Actuator system according to any of the preceding claims,
   characterized in that
   a first electrode segment (42, 43) is electrically conductively connected to the first internal electrodes (5) in a first and a second actuator section (82, 83; 84, 85) adjacent thereto, and in that a second electrode segment (21, 22) is electrically conductively connected to the second internal electrodes (3) in the second and in a third actuator section (82, 81; 84, 83) adjacent thereto.
5. Actuator system according to any of the preceding claims,
   characterized in that
   at least the electrode segments (21, 22, 23) of the second external electrode (2) in each case comprise a terminal (210, 220, 230), to which a control signal (U1, U2, U3, U4, U6) can be applied.
6. Actuator system according to any of the preceding claims,
   characterized in that
   the control arrangement (6) is suitable for applying voltages (U1, U2, U3, U4, U5, U6) having different signs relative to a reference-ground potential (7) to the electrode segments (41, 42, 43) connected to the first internal electrodes (5) and the electrode segments (21, 22, 23) connected to second internal electrodes (3).
7. Actuator system according to any of the preceding claims,
   characterized in that
   the time shift is dependent on the velocity of sound in the actuator (1).
8. Method for the control of an actuator (1), which is expandable in a predefined direction, comprising piezoelements (16) arranged in a stacked fashion, first and second internal electrodes (5, 3) arranged alternately between the piezoelements (16), wherein the actuator (1) comprises a multiplicity of actuator sections (81, 82, 83, 84, 85) comprising a first actuator section (81, 82, 83, 84, 85), which is arranged in the predefined direction relative to a second actuator section (81, 82, 83, 84, 85), and a first control voltage is applied between the first and second internal electrodes (5, 3) in the first actuator section (81, 82, 83, 84, 85) or in a first group of actuator sections (81, 82, 83, 84, 85) in a time-shifted manner with respect to a second control voltage applied between the first and second internal electrodes (5, 3) in the second actuator section (81, 82, 83, 84, 85) or in a second group of actuator sections (81, 82, 83, 84, 85) in such a way that the first control signal (U1, U2, U3, U4, U5, U6) is at the first actuator section or the first group of actuator sections in a time-delayed manner with respect to the second control signal (U1, U2, U3, U4, U5, U6) at the second actuator section or the second group of actuator sections, so that the elastic partial waves generated by the control signals during the expansion of the actuator in the respective actuator sections or groups of actuator sections are superimposed.
9. Control method according to Claim 8,
   characterized in that
   the actuator (1) is expandable in one direction, wherein the first actuator section (81, 82, 83, 84, 85) is arranged in the direction relative to the second actuator section (81, 82, 83, 84, 85), and wherein the first control voltage is time-delayed with respect to the second control voltage.
10. Control method according to Claim 8 or 9,
    characterized in that
    the time shift is chosen in a manner dependent on the velocity of sound in the actuator (1).

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